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 Post subject: Breaker failure and LOTO
PostPosted: Fri Jun 19, 2009 3:21 pm 
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Joined: Fri Jun 19, 2009 3:06 pm
Posts: 2
Location: Oregon
When performing the voltage test on a breaker for LOTO, what energy level is considered?

Case 1: Assume the breaker was inadvertantly left open. You would use the energy level from the load side of the breaker.

Case 2: Assume the breaker failed and one phase stayed closed in and will not open in case of and arc flash. You would use the energy level from the line side of the breaker.

Obviously case 2 is more conservative. I just don't remember NFPA 70E talking about assuming one level of failure in the analysis. It just says to consider the conductor energized until placed in an electrically safe work condition.

Thanks for any insight...


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PostPosted: Fri Jun 19, 2009 7:00 pm 
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Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
mascott wrote:
When performing the voltage test on a breaker for LOTO, what energy level is considered?

Case 1: Assume the breaker was inadvertantly left open. You would use the energy level from the load side of the breaker.

Case 2: Assume the breaker failed and one phase stayed closed in and will not open in case of and arc flash. You would use the energy level from the line side of the breaker.

Obviously case 2 is more conservative. I just don't remember NFPA 70E talking about assuming one level of failure in the analysis. It just says to consider the conductor energized until placed in an electrically safe work condition.

Thanks for any insight...



You assume the breaker is closed and will do its job. That is the scary thing is all arc flash studies are assuming the OCPD will work right, thats why they added the testing of OCPD'd per the 70B or ANSI/NETA MTS to the "Safety related maintenence practices" section of the 70E. Basicaly your analysis assumes the breakers will work right but your study is invalid if you dont test your breakers.


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